1. Field of the Invention
The present invention relates to a heat processing method and apparatus for a semiconductor process for performing a heat process to form an oxide film or oxynitride film on a target substrate, such as a semiconductor wafer. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an FPD (Flat Panel Display), e.g., an LCD (Liquid Crystal Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing semiconductor integrated circuits, a semiconductor substrate, such as a silicon wafer, is subjected to various processes, such as film formation, etching, oxidation, diffusion, and reformation, in general. For example, oxidation includes oxidation of the surface of a mono-crystalline silicon film or a poly-crystalline silicon film, and oxidation of a metal film. Particularly, a silicon oxide film formed by oxidation is applied to a device isolation film, gate oxide film, capacitor insulating film, or the like.
As regards methods for performing an oxidation process, where locking at them by the type of pressure, there is a normal-pressure oxidation method, in which the atmosphere inside a process container is set to be almost equal to atmospheric pressure. Further, there is a low-pressure oxidation method, in which the atmosphere inside a process container is set to be a vacuum. Where looking at them by the type of gas used for oxidation, there is a wet oxidation method, in which, for example, hydrogen and oxygen are burnt in an external combustion apparatus to generate water vapor, so as to perform oxidation by use of the water vapor (for example, Jpn. Pat. Appln. KOKAI Publication No. 3-140453 (Patent Document 1)). Further, there is a dry oxidation method, in which ozone or oxygen is solely supplied into a process container to perform oxidation without using water vapor (for example, Jpn. Pat. Appln. KOKAI Publication No. 57-1232 (Patent Document 2)).
As described above, oxidation can be performed by dry oxidation that employs oxygen gas, or wet oxidation that employs water vapor. In general, an oxide film formed by wet oxidation is higher in film quality than an oxide film formed by dry oxidation. Accordingly, in consideration of film properties, such as breakdown voltage, corrosion resistance, and reliability, a wet oxide film is better as an insulating film. On the other hand, the film formation rate of an oxide film (insulating film) to be formed and the planar uniformity therein on a wafer are also important factors. In this respect, a film formed by wet oxidation under a normal pressure shows a high oxidation rate, but shows poor planar uniformity in film thickness, in general. By contrast, a film formed by wet oxidation under a vacuum pressure shows a low oxidation rate, but shows good planar uniformity in film thickness.
Where the design rule of semiconductor devices or semiconductor integrated circuits is not so strict, various oxidation methods as those described above are selectively used, in consideration of, e.g., the intended purpose of oxide films, process conditions, and apparatus cost. On the other hand, in recent years, the line width and film thickness of semiconductor devices have decreased, and thus the design rule has become stricter. This tendency has given rise to demands on better planar uniformity in the quality and thickness of oxide films. However, conventional oxidation methods are now becoming inadequate in this regard, because they cannot sufficiently fulfill the demands.
Jpn. Pat. Appln. KOKAI Publication No. 4-18727 (Patent Document 3) discloses an oxidation apparatus utilizing a wet oxidation method. According to this apparatus, H2 gas and O2 gas are respectively supplied into the bottom of a vertical reaction tube made of quartz and are burnt in a combustion section formed in a quartz cap to generate water vapor. This water vapor flows upward along the array of wafers and performs an oxidation process on the wafers. In this case, since H2 gas is burnt in the combustion section, the bottom of the process container near there is rich in water vapor. On the other hand, the top of the process container is poor in water vapor, because the water vapor is consumed while it flows upward. Consequently, the thickness of an oxide film formed on the wafers may vary greatly depending on the wafer support positions of the wafer boat, thereby deteriorating the inter-substrate uniformity in the oxide film thickness.
According to the apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 57-1232 (Patent Document 2) described above, a horizontal reaction tube of the batch type is used to array a plurality of semiconductor wafers side by side. O2 gas is solely supplied or O2 gas and H2 gas are supplied at the same time from one side of the reaction tube to form an oxide film within a vacuum atmosphere. This apparatus is arranged to perform film formation within an atmosphere having a relatively high pressure by use of a hydrogen burning oxidation method, so the reaction is caused mainly by water vapor components. In this case, the concentration of the water vapor may vary greatly between the upstream side and downstream side of the gas flow inside the process container, thereby deteriorating the inter-substrate uniformity in the oxide film thickness, as in the case described above.
U.S. Pat. No. 6,037,273 (Patent Document 4) discloses an oxidation apparatus of another type. According to this apparatus, oxygen gas and hydrogen gas are supplied into a process chamber of the single-substrate type provided with heating lamps. These gases react with each other to generate water vapor near the surface of a semiconductor wafer placed inside the process chamber, so that silicon on the wafer surface is oxidized by this water vapor to form an oxide film.
However, according to this apparatus, oxygen gas and hydrogen gas are delivered into the process chamber from gas inlet 20 to 30 mm distant from the wafer, and react with each other to generate water vapor near the surface of the semiconductor wafer. Further, the process pressure is set at a relatively high value. These conditions may deteriorate the planar uniformity in the oxide film thickness.
Jpn. Pat. Appln. KOKAI Publication No. 2002-176052 (Patent Document 5) discloses an oxidation method of another type. According to this method, an oxidizing gas, such as O2 gas, and a deoxidizing gas, such as H2 gas, are supplied into a process chamber at the same time and react with each other within a vacuum atmosphere. Consequently, oxygen radicals and hydroxyl group radicals are generated and serve as the main part of the atmosphere, within which silicon wafers or the like are oxidized.
Jpn. Pat. Appln. KOKAI Publication No. 2000-183055 (Patent Document 6) discloses a method for forming an oxynitride film (SiON film) with high quality, as an insulating film other than the oxide film. According to this method, an SiO2 film formed by, e.g., one of those methods described above is subjected to a nitridation process by use of ammonia, nitrogen monooxide (NO), or dinitrogen oxide (N2O), thereby forming an SiON film. After the nitridation process, a re-oxidation process is performed by use of, e.g., O2 gas to remove excessive N components.